The practice of chiropractic care focuses on the relationship between the body’s structure, primarily the spine, and its function, mainly the nervous system. Chiropractors use manual techniques to diagnose and treat mechanical disorders of the musculoskeletal system. This article reviews the objective scientific literature, including randomized controlled trials and systematic reviews, to determine the evidence base for common chiropractic interventions.
The Primary Intervention: Spinal Manipulative Therapy
The core procedure evaluated by scientific studies is Spinal Manipulative Therapy (SMT), often called a spinal adjustment. SMT is defined as a high-velocity, low-amplitude thrust (HVLAT) applied to a joint, moving it slightly beyond its typical physiological range of motion without exceeding the anatomical limit. This thrust is typically delivered to a specific joint in the spine.
This maneuver often produces an audible “pop” or “crack,” known as cavitation, caused by the sudden release of gas within the joint’s synovial fluid. The primary goal of SMT is to restore normal joint mobility, which may have been restricted by injury or tissue changes. Neurophysiological effects, such as pain reduction through altered nerve signaling, are also hypothesized mechanisms of action.
Scientific Evidence for Musculoskeletal Pain
Scientific evidence most consistently supports the use of SMT for common musculoskeletal complaints, particularly in the spine. Clinical practice guidelines frequently recommend SMT as a treatment option for low back pain (LBP) and neck pain.
For acute low back pain, meta-analyses suggest that SMT provides modest improvements in pain and function for up to six weeks. SMT is superior to sham treatments, but its effectiveness is comparable to other standard interventions, such as physical therapy or prescribed exercises. For chronic low back pain, moderate-quality evidence indicates that SMT produces similar effects to other guideline-recommended therapies for short-term pain relief.
Evidence regarding neck pain is similarly favorable, especially when SMT is applied with other therapies. SMT is considered effective for acute and subacute neck pain, and combining manipulation with exercise appears beneficial for chronic neck pain. Guidelines have increasingly favored SMT for specific types of headache, such as cervicogenic headache.
Studies suggest SMT can reduce the frequency and intensity of cervicogenic headaches, although some randomized trials are limited by small sample sizes. The efficacy of SMT for these spine-related conditions underscores its role as a non-pharmacological option for pain management.
Scientific Evidence for Non-Spinal Conditions
For conditions not directly related to mechanical musculoskeletal issues, the scientific evidence supporting SMT is significantly weaker. Pediatric conditions, such as infantile colic, are frequently cited by practitioners, but high-quality evidence remains limited.
Systematic reviews on infantile colic have yielded conflicting results. Some reviews find chiropractic care viable, while others conclude that robust clinical trials fail to demonstrate a benefit beyond placebo or the condition’s natural resolution. One large randomized controlled trial found that decreased crying duration was not statistically significant after adjusting for baseline factors.
For otitis media (middle ear infections), the evidence is primarily composed of case studies and older pilot studies showing a correlation with improved symptoms. However, there is a lack of high-quality randomized controlled trials to establish efficacy.
For systemic conditions like hypertension and asthma, the current literature does not support SMT as a primary treatment. Systematic reviews on spinal manipulation for hypertension have found insufficient low-bias evidence to support its use as a therapeutic option. While some studies show a decrease in systolic blood pressure, those trials often carry a higher risk of bias, and low-bias studies show no significant advantage over sham treatment.
Randomized controlled trials demonstrate that SMT does not produce statistically significant changes in objective lung function measures for asthma, such as forced expiratory volume (FEV1) or peak flow. Any reported benefits are restricted to subjective measures, such as self-reported quality of life or symptom severity. SMT should not be a replacement for conventional medical care for systemic diseases.
Safety Data and Reported Adverse Events
SMT carries potential adverse events, which are generally categorized into common, mild side effects and rare, serious complications. Common, mild side effects are frequently reported and include temporary local soreness, stiffness, and headache, which typically resolve within 24 hours. These minor events occur in a substantial number of patients, with estimates ranging from 30% to 67%.
The most serious concern involves cervical manipulation and the rare risk of vertebral artery dissection (VAD) leading to stroke. The estimated incidence of a serious adverse event following cervical manipulation is highly variable, ranging from one in 250 million to as high as one in 20,000 manipulations.
Large population-based studies suggest that the association between cervical SMT and VAD may be coincidental rather than causal. Patients experiencing VAD often present with neck pain and headache, leading them to seek care just before the stroke occurs naturally. This suggests that the patient’s existing vascular pathology, rather than the manipulation, is the primary cause of the event. Absolute contraindications, such as bone tumors or unstable fractures, make SMT unsafe and necessitate careful screening before treatment.